Even then working from disassembler output is very difficult. Modern compilers perform a number of optimizations producing assembler instructions that obscure the function of the code. You don't mention how much experience with C and systems programming you have, but any non-trivial program will do most of its work through system calls and libraries--you will need to under stand these before you can make much sense of the code.

On top of all that, there are many uses for disassemblers that are malicious, violate software licenses, illegal or unethical. We tend to avoid answers to questions like that.